[GitHub] takumiCX opened a new issue #353: CompositeOmegaCallback的compensate(TxEvent event)方法有并发问题

[GitBox <gi...@apache.org>]

takumiCX opened a new issue #353: CompositeOmegaCallback的compensate(TxEvent event)方法有并发问题
URL: https://github.com/apache/servicecomb-pack/issues/353
 
 
   CompositeOmegaCallback类的public void compensate(TxEvent event)方法可能会有并发异常
   
   > public void compensate(TxEvent event) {
   >     Map<String, OmegaCallback> serviceCallbacks = callbacks.getOrDefault(event.serviceName(), emptyMap());
   > 
   >     if (serviceCallbacks.isEmpty()) {
   >       throw new AlphaException("No such omega callback found for service " + event.serviceName());
   >     }
   > 
   >     OmegaCallback omegaCallback = serviceCallbacks.get(event.instanceId());
   >     if (omegaCallback == null) {
   >       LOG.info("Cannot find the service with the instanceId {}, call the other instance.", event.instanceId());
   >       omegaCallback = serviceCallbacks.values().iterator().next();
   >     }
   > 
   >     try {
   >       omegaCallback.compensate(event);
   >     } catch (Exception e) {
   >       serviceCallbacks.values().remove(omegaCallback);
   >       throw e;
   >     }
   >   }
   > 
   
   考虑serviceCallbacks这个map不为空,恰好只有一个元素<instance-1,omegaCallback>的情形,当该线程刚好通过下面这部分代码的if条件时让出cpu执行权
   
   >  if (omegaCallback == null) {
   >       LOG.info("Cannot find the service with the instanceId {}, call the other instance.",    event.instanceId());
   >       omegaCallback = serviceCallbacks.values().iterator().next();
   >     }
   
   此时刚好收到来自omega端的一个onDisconnected请求,instanceId恰好就是上面map里的instance-1
   
   
   > public void onDisconnected(GrpcServiceConfig request, StreamObserver<GrpcAck> responseObserver) {
   >     OmegaCallback callback = omegaCallbacks.getOrDefault(request.getServiceName(), emptyMap())
   >         .remove(request.getInstanceId());
   > 
   >     if (callback != null) {
   >       callback.disconnect();
   >     }
   > 
   >     responseObserver.onNext(ALLOW);
   >     responseObserver.onCompleted();
   >   }
   
   导致serviceCallbacks这么map中instance-1对应的Entry被移除, 导致map为空,当执行compensate的线程继续执行
   
   > serviceCallbacks.values().iterator().next();
   
   将抛出下面的异常
   
   > Exception in thread "Thread-1" java.util.NoSuchElementException
   > 	at java.util.concurrent.ConcurrentHashMap$ValueIterator.next(ConcurrentHashMap.java:3436)
   > 	at org.apache.servicecomb.saga.alpha.core.CompositeOmegaCallback.compensate(CompositeOmegaCallback.java:64)
   > 	at org.apache.servicecomb.saga.alpha.core.CompositeOmegaCallbackTest$1.run(CompositeOmegaCallbackTest.java:171)
   > 	at java.lang.Thread.run(Thread.java:748)
   
   
   

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